In air conditioners and refrigerators, an electric compressor equipped with an electric motor is used in order to compress a refrigerant. For the motor of the electric compressor, a magnet-embedded-type electric motor is used, which is provided with a rotor in which a plurality of permanent magnets are embedded at predetermined intervals in the circumferential direction on the outer periphery of a rotor iron core formed by laminating magnetic steel plates.
This electric motor includes a stator and the rotor, which is disposed on an inner side of the stator with a predetermined gap therebetween. The rotor has a structure in which a plurality of main magnetic poles, provided with magnet insertion holes in which permanent magnets are embedded, and a plurality of auxiliary magnetic poles (auxiliary salient poles), formed by iron core portions located between the main magnetic poles, are alternately disposed in the circumferential direction in a plane perpendicular to the axial direction. Thus, a rotating torque is obtained by using both a magnetic torque generated by the magnetic flux of the permanent magnets and a reluctance torque generated by salient-pole characteristics of the auxiliary magnetic poles and the main magnetic poles.
In such electric motors, PTLs (Patent Literatures) 1 and 2 etc. propose electric motors equipped with a rotor in which a magnet insertion hole is provided for each of the main magnetic poles in the rotor iron core, the magnet insertion hole having substantially a V-shape whose convex portion faces the center of the rotor and is centered on a d-axis that passes through the center of the rotor and the circumference-wise center of the main magnetic pole, and two permanent magnets per pole are embedded in the magnet insertion hole in a substantially V-shaped manner.